1. Field of the Invention
The present invention relates to a method of correcting measurement data of a coordinate measuring machine and a coordinate measuring machine. In particular, the present invention relates to a method of correcting measurement data when probes having different weights are attached to a ram of a coordinate measuring machine and a coordinate measuring machine.
2. Description of Related Art
A typical coordinate measuring machine includes a table on which an object is to be mounted, a ram that has an end attached with a probe in an exchangeable manner, and a movement mechanism that causes a relative movement between the ram and the table in a three-dimensional direction (X-, Y- and Z-axis directions).
Such a coordinate measuring machine suffers an error (geometric error) resulting from a geometric factor such as a deformation in the movement mechanism. Examples of the error are an error in the scale of each axis, an error in the horizontal straightness of each axis, an error in the vertical straightness of each axis, a pitching error in each axis, a yawing error in each axis, a rolling error in each axis and angular errors between the axes.
In order to correct such a geometric error, a coordinate measuring machine disclosed in Patent Literature 1 (JP-A-7-146130) performs volumetric measuring accuracy correction to correct an error at a reference position (datum point) defined in a ram (movement mechanism). Measurement data is calculated by compositing a probe vector (position vector) from the reference position to the position of a probe end and the corrected reference position, the probe vector being calculated by measuring a center position (reference coordinates) of a reference sphere provided in a measurement space.
Generally, various probes, such as a contact probe (e.g., a contact probe for point measurement or scanning measurement) and a non-contact probe, are selectively used depending on conditions such as the material of an object and a required accuracy. Since probes with various characteristics are different in shape and size from one another, their respective weights are also different.
Thus, in the coordinate measuring machine disclosed in Patent Literature 1, when probe exchange is carried out, an error in measurement data cannot be sufficiently corrected because the weight of the probe changes and thus the reference position also changes.